This invention relates to an apparatus and method for substantially improving the viscosity measuring performance of viscometers and rheometers of the oscillatory type when used in the presence of ambient noise and/or vibration. The invention is especially suitable for, but not limited to, use with inline viscometers in process control applications; and is particularly effective in viscometer and rheometer devices employing oscillation sensors of the types disclosed in U.S. Pat. Nos. 4,524,610, 4,566,181 and 4,754,640, as well as U.S. patent application Ser. No. 07/348,695.
In process control applications in manufacturing or processing plants, pump, machinery and pipe vibration adversely affects the accuracy of viscosity measurement by oscillatory viscometers and rheometers; devices which are otherwise capable of high precision. In a factory, viscosity of fluid materials is often measured at high temperatures and pressures while the materials are passing through vibrating pipes. This environment produces noisy electronic signals in most instrumentation, including oscillatory (also known as vibratory) viscometers, and gives rise to erratic and erroneous readings.
When the viscosity of the fluid is high, e.g. 1,000 to 1,000,000 centipoise and more, the amplitude of the signal produced by a vibratory viscometer is generally relatively high in comparison to the background noise caused by factory vibrations. Thus the effects of noise and vibration are generally tolerable in instruments intended for measurements at such high viscosity levels.
On the other hand, when the viscosity range is low, e.g. 1 to 100 centipoise, as it is for many liquids such as solvents, fuels and monomers, mechanical disturbance from pumps, nearby moving vehicles and machinery can produce erroneous signals that seriously interfere with the viscosity measurement. These conditions are so severe that inline viscosity measurements at these low values have frequently been viewed as having no significant benefit.
Accordingly, an object of the present invention is to provide an apparatus and method capable of accurate inline measurement of viscosity in the presence of extraneous noise and vibration.